diamond MESFETs fabricated on hydrogenated polycrystalline diamond. The devices under examination
have a coplanar layout with two gate fingers, total gate periphery of 100 lm; in DC they exhibit a hole
accumulation behavior with threshold voltage Vt 0–0.5 V and maximum drain current density of
120 mA/mm. The best small-signal radio frequency performances (maximum cutoff or transition frequency
fT and oscillation frequency fmax) were obtained close to the threshold and were of the order of
6 and 15 GHz, respectively. The power radio frequency response was characterized by driving the devices
in class A at an operating frequency of 2 GHz and identifying through the active load-pull technique the
optimum load for maximum power added efficiency. A power gain in linearity of 8 dB and an output
power of approximately 0.2 W/mm with 22% power added efficiency were obtained on the optimum load
impedance at a bias point VDS = 14 V, VGS = 1 V. To the best of our knowledge, these are the first large
signal measurements ever reported for surface MESFET on polycrystalline diamond, and show the potential
of such technology for the development of microwave power devices.

diamond MESFETs fabricated on hydrogenated polycrystalline diamond. The devices under examination
have a coplanar layout with two gate fingers, total gate periphery of 100 lm; in DC they exhibit a hole
accumulation behavior with threshold voltage Vt 0–0.5 V and maximum drain current density of
120 mA/mm. The best small-signal radio frequency performances (maximum cutoff or transition frequency
fT and oscillation frequency fmax) were obtained close to the threshold and were of the order of
6 and 15 GHz, respectively. The power radio frequency response was characterized by driving the devices
in class A at an operating frequency of 2 GHz and identifying through the active load-pull technique the
optimum load for maximum power added efficiency. A power gain in linearity of 8 dB and an output
power of approximately 0.2 W/mm with 22% power added efficiency were obtained on the optimum load
impedance at a bias point VDS = 14 V, VGS = 1 V. To the best of our knowledge, these are the first large
signal measurements ever reported for surface MESFET on polycrystalline diamond, and show the potential
of such technology for the development of microwave power devices.